Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-10-18
2004-02-17
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S436000, C455S445000, C370S318000, C370S329000, C370S332000
Reexamination Certificate
active
06694147
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications systems and, more particularly, to methods and apparatus for communicating between base stations and mobile stations.
BACKGROUND OF THE INVENTION
Several technologies are competing to provide wireless data and/or voice service. Competing technologies include the Third Generation (
3
G) wireless standard which uses Code Division Multiple Access (CDMA); High Data Rate (HDR) by Qualcomm; and Flash-OFDM by Flairion Technologies the assignee of the present application. Such services confront similar problems concerning efficient allocation of communication resources between individual base stations (BSs) and the mobile stations (MSs) served by an individual BS. Consider the downlink of a wireless communication system. Here a single BS communicates with a set e.g., plurality, of MSs. The information transmitted to the users comes with certain delay and rate requirements. For example, voice has a constant but fairly small rate requirement and fairly stringent delay requirements. Data traffic e.g., Internet downloads, streaming video, file transfers, on the other hand, have requirements that vary from the type of traffic and can be very bursty in nature as compared to voice traffic. Thus, allocating a constant rate channel permanently to a user is usually wasteful in terms of resources. In view of the above discussion, there is a need for improved methods and apparatus for allocating bandwidth between users.
SUMMARY
The present invention is directed to methods and apparatus for enhancing overall throughput in communications systems, e.g., mobile communications systems, wherein some flexibility in the scheduling of transmission times to users corresponding to, e.g., different stations, is possible. Scheduling users when data comes to them results in a more flexible use of the system resources, e.g., power and bandwidth, than constantly allocating them a fixed amount of resource as is generally done in the cellular telephone where live audio conversations are being supported.
In the present application, communications stations used by system users are referred to herein as mobile stations (MS) since the invention is described in the context of a mobile communications system. However, it is to be understood that the techniques of the present invention can be applied where channel conditions may vary. Accordingly, the techniques of the present invention can be applied to both mobile as well as stationary communications stations.
In accordance with one embodiment of the present invention a base station (BS) transmits data to various MSs. The BS decides which MS to transmit to at any given time. Assuming that information, e.g., data, needs to be transmitted to multiple MSs, it is the responsibility of the BS to arbitrate between the needs of the MSs and decide when and for how long data is to be transmitted to each MS. This process is sometimes referred to as scheduling, since data is scheduled for transmission to various MSs. As part of the scheduling process, the base station may allocate bandwidth, e.g., a range of frequencies to be used, and the amount of power to be used for transmission purposes.
The MSs of the present invention provides feedback to the BS regarding channel conditions. In accordance with one feature of the present invention, data to be transmitted to MSs is scheduled based on channel condition feedback information obtained by MSs. When channel conditions are good, data can, and is, transmitted at a higher rate, e.g., bits(s), than when channel conditions are bad. By factoring in channel condition information, data transmission to MSs is scheduled so that transmission will occur when an MS is experiencing good channel conditions, e.g., conditions permitting relatively few errors and thus high transmission rates. In accordance with the present invention, scheduling based on how good a channel each mobile station (MS) has is used to achieve greater overall BS throughput than, e.g., scheduling of transmissions in a round robin, or a random order independent of MS channel conditions.
In order to insure that each user will receive some data even when experiencing poor channel conditions for an extended period of time, in accordance with various embodiments of the invention the scheduling of data transmission to MSs may take into consideration factors other than channel conditions alone. For example, when users have high priority, e.g., because these users have paid more for the service, and/or if a user's applications have stringent delay requirements, e.g., as in the case of, streaming video, then the base station (BS) may schedule users even when their channel is not as good as desired or when it is worse than another user's channel. Overall BS throughput may take a hit under such circumstances as compared to embodiments which schedule transmission times solely or primarily based on channel conditions. This is particularly the case when there are stationary users who do not have a good channel.
In the case of a non-moving MS or fixed position user station, actual physical channel conditions may remain relatively constant over time.
In accordance with one feature of the present invention each BS creates an artificial channel variation, e.g., by transmitting the same information using different transmitters which are physically spaced apart. Assuming two transmitters, e.g., antennas are used, the first transmitter broadcasts a first signal with a first information, e.g., data content, while the second transmitter transmits a second signal with the same information content but with a different phase and/or amplitude. The difference, e.g., phase and/or amplitude, between the first and second signals is varied over time. At the receiver, the first and second signals interact and are interpreted as a single received signal. The amplitude of the received signal is measured and feed back to the BS as an indication of the channel conditions existing between the BS and MS.
Thus the BS can schedule the MS as a function of the feedback information including channel state information. As discussed above, the feedback information is then used as part of a general strategy of scheduling the user when the channel associated with the user's MS becomes good enough. This strategy can be used to improve the throughput of the downlink and is efficient even when some MSs are stationary and thus their channels tend not to be naturally changing.
The strategy of the present invention used in the context of one mobile communications system embodiment is as follows: We have n antennas at the BS and we multiply the signal (which is a complex number in the base band representation) that is sent to the MSs by complex numbers, e.g., scaling factors, a
1
, . . . , a
n
and send them on the air over the n antennas. These complex numbers may be, and in at least one embodiment are, chosen randomly in each time segment data is transmitted. Some desired, but not mandatory, properties of these complex scaling factors a
1
, . . . , a
n
are as follows:
1. The sum of magnitude squared of the a
i
over a period of time, e.g., symbol period or multiple carrier signal periods, is equal to a constant.
2. From time segment to time segment, the complex scaling factors change in a continuous manner. This makes it easier for the receiver to track the channel variation and feed back a reliable estimate of the channel strength.
The artificial signal variation introduced through the BS transmitting the same information signal from multiple transmitters is something the BS can track using the channel condition feedback information obtained from the MSs. Accordingly, the BS can use this variation, in addition to actual channel variations, to schedule the MS when its channel is indicated as being good. As part of the scheduling process, in some embodiments, more bandwidth is allocated to MSs when their channel conditions are good than when they are poor. In addition, as part of the scheduling process, in some embodiments more power is allo
Laroia Rajiv
Tse David N. C.
Viswanath Pramod
D'Agosta Stephen
Flarion Technologies, Inc.
Straub Michael P.
Straub & Pokotylo
Trost William
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